Cuprammonium cellulose film

ABSTRACT

Thin cellulose hydrate films, having a superficial density of less than 15 gms. per square metre, for example, 10, 8, 6, and even 5 gms. per square metre, are obtained by extruding cuprammonium cellulose solution under pressure through narrow slots of 0.05 mm. to 0.5 mm. width, drawing out to the desired thinness through a coagulating or precipitating bath of dilute caustic soda, passing by means of suitable rotating transport appliances through the necessary after-treatment baths, and if necessary, drying on a system of heated rollers.  The structure of cuprammonium cellulose solution issuing from the extrusion appliance may be led first through an air gap of a few millimetres and then through a stretch of free precipitating bath amounting to several centimetres, after which it is allowed within this bath to run on to a drum of comparatively large diameter (e.g. 1 metre), to which it may be caused to adhere by endless bands, to prevent transverse shrinkage, and passed on to further treatment on subsequent transport appliances.  The coagulated film is preferably allowed to run on to a drum of large diameter at the point of entry into the first acid bath.  In an example, the solution comprises 7.2 per cent of cellulose, 7 per cent of ammonia, and 3.5 per cent of copper and the width of the extrusion slot is 0.15 mm.  The shaped solution passes first through air for 5 mm., and then freely through a 4.5 per cent soda lye for 16 cm. The partially coagulated film is supported on a rotating drum of 1 m. diameter during the remainder of the coagulation treatment, and then passed on to further treatment successively with water, 10 per cent sulphuric acid, water and glycerine.  The total stretch amounts to about 300 per cent, and the rate at which the film leaves the last bath, about 10 m. per minute.

R. ETZKORN ET AL 2,035,645

CUPRAMMONI'UM CELLULOSE FILM March 31, 1936.

Original Filed Aug. 26, 1935 INVENTORS WIT uoou ETZ KORN EW/VLO KNEHEflLgBY ATTORNEYS Patented Mar. 31, 1936 UNITED STATES PATENT OFFICECUPRAMMONIUM CELLULOSE FILM Rudolf Etzkorn and Ewald Knehe, Wuppertal-Barmen, Germany, assignors to I. P. Bembery Aktiengesellschaft,

Wuppertal Oberbarmen,

Germany, a corporation of Germany ber 3, 1932 7 Claims. (CI. 1857) Thepresent invention relates to theproduction of films from copper oxideammonia cellulose solution of unusual thinness and having novel andimproved properties.

It is the object of this invention to provide a method of making thinnerthe freshly spun foils obtained by squirting out a cuprammoniumcellulose solution by stretching before complete coagulation has takenplace, and by avoiding thickening of the film by transverse shrinkageduring the after treatment.

Further objects of the invention will become apparent from a perusal ofthe following description and the drawing in which is diagrammaticallyshown in cross-section an apparatus for carrying out the process inpractice.

The present application is a division of our application Serial No.687,001, filed August 26, 1933.

There is aneed for an extremely thin, absolutely transparent cellulosehydrate foil possessing only an extremely small weight per square meter.The finest cellulose hydrate foils now on the market have a thickness ofa minimum of 0.02 mm. and consequently a weight per square meter ofgrams. The other brands have a considerably greater weight. For manifoldpurposes, however, this thickness of the foil has proved to be much toohigh and accordingly unusable for the purposes in view, especially asthe finest gauge sheets heretofore made have been manufactured fromviscose and have only a comparatively small degree of toughness.

Thus, there exists a demand for extremely fine cellulose hydrate foils,for example for the binding of bass strips in the manufacture of hatmaterial. The finest, thinnest cellulose hydrate foils used theretofore,even of a weight of only 30 grams per square meter, burden the boundhemp far too much and the flexibility is too slight. In the other usesof cellulose hydrate foils itis a question of covering and liningobjects of an uneven surface in such a manner that the contours can beapparent through the cellulose hydrate. For these purposes even thethinnest cellulose hydrate foils made heretofore are not utilizable,because they are too thick, too stiff, too glass-like and too littleplastic.

The most diverse ways have been tried in order to produce a film fromcellulose hydrate which is extremely fine, clear as glass and much finerthan the finest gauges produced up to now. Particularly the methodsapplied heretofore in the industry of working up viscose with or withoutthe use of a pouring base did not lead to the goal nor to any usableproduct.

1 slits of 0.05 to 0.5 mm. width of slit and the nap is drawn off bymeans of delivery rollers through a coagulating or precipitating bath ofdiluted soda lye and, if desired, stretched to the required fineness,and the structure then by suitable rotating transport devices conductedthrough the necessary after-treatment baths for washing, acidifying andloading with glycerine, and if necessary then dried in a manner knownper se over a system of drying cylinders and finally the thus obtainedfilm is sub-divided in the desired way directly or after previouswinding. I

Tests have proved that it is preferable not to allowthe so-called.pourer or hopper to dip into the precipitating bath. The reason for thisis to be found in coagulation on the pouring slit, which can lead tostopping up the slit.

Now in order to remedy the defects spoken of and to eifectuate a properprecipitation of the nap coming from the'slit, the nap is conductedthrough a stretch of air measuring a few millimeters and thereuponthrough a free bath passage measuring several centimetersnand thenallowing the film to run inside the bath onto a drum of comparativelylarge circumference, which by adhesion prevents the nap, as itsolidifies into a film, from shrinking transversely and thereupon thefilm is passed for further treatment to the subsequent transportelements.

The stretch of air is chosen best as small as possible. It has beenfound that a distance of 1 to 10 millimeters between the slit and thelevel of the precipitating bath is best. The smaller values will beavailed of when the surface of the precipitation bath is practicallycalm and the greater distances wheh the surface of the precipitatingbath is not quite s6 calm. If the stretch of air is too large the napissuing from the slit contracts towards the center, and in addition anaccumulation of material takes place at both sides of the nap, whichproduces a thickening of the film at the edges.

The free bath passage is bestchosen at a length of about 10 to 20 cm. Bythis means the coagulation takes place at both sides of the nap. Toolong a free precipitating bath passage is to be avoided on account ofthe transverse shrinkage setting in when the nap solidifies into a film.This preliminary coagulation of the film while unsupported on eitherside insures a product which is substantially equally smooth on bothsides, as distinguished from a process in which a cellulose solution ispoured upon a surface, the solvent permitted to evaporate and the driedfilm then stripped off, the film in such case being relatively rough onits supported side.

The drum, onto which the film or band is allowed to run after passingthrough the free stretch of bath, is made comparatively large, for thegreater the circumference of the drum, the smaller the angular speed ofthe drum is able to be kept. Drums of a diameter of cm. are adequate. Itis, however, preferable to use drums of a diameter of 1 meter or more.

The transverse shrinkage of the film is prevented extensively by thedrum. This is due to the fact that the film, owing to adhesion, adheresfirmly to the surface of the drum. By utilizing the known endlesspress-on bands or by other devices opposing the transverse shrinkage ofthe film the efi'ect of the adhesion force can be still considerablyincreased.

An appreciable transverse shrinkage of the film takes place not onlydirectly after the pouring but also on entrance of the film into thefirst acid bath. It is, therefore, advisable to provide also in suchbath a drum with a comparatively large circumference, which can also beused in combination with endless press-on bands in the same manner asthe first large drum. The diameter of the usual transport rollers, withwhich the film is transported, preferably in an up and down direction,through the various after-treatment baths, is of relatively smallimportance, even though it is also advisable not to make the diameter ofthese too small. Of great importance, however, are the dimensions of thejust described two drums, the one arranged directly after the pourer andthe other at the entrance of the film into the first acid bath, becauseon these two places the symptoms of transverse shrinkage areparticularly great.

Inter alia a composition of 7.2% cellulose, 7% ammonia and 3.5% coppercan be used as the copper-containing spinning solution.

The drawing shows diagrammatically a device adapted for the productionof films according to the invention. The spinning solution with acomposition just described. is squirted by air pressure or suitablepumps in the manner well known in the production of viscose films out ofa slot of a pouring device or hopper a which is adjusted to a width of0.15 mm. The nap thus formed is, however, not introduced directly intothe coagulating liquid but first passes through a stretch of air I) of 5mm. Hereupon it enters a coagulating bath 0 consisting of 4.5% soda lye.The nap is conducted through the free 16 cm. long bath stretch d andthus coagulated from both sides. The pre-coagulated film is then allowedto run on the drum e having a diameter of 1 meter. The outside edges ofthe film lying on the drum are pressed onto the drum by the press-onbands I, so that a transverse shrinkage of the film during the firststeps of coagulation is avoided. The film is then released from the drumand is conducted further through the coagulation bath coilwise overrollers g each of a diameter of 10 cm. Thereupon follows anafter-treatment with pure water in the trough h and an acidifyingtreatment in trough i to remove copper and other impurities. The tank 2'contains 10% solution of sulphuric acid. As the film in the acidtreatment also has a strong tendency to shrink, care is taken accordingto the invention to prevent such shrinking. This is done by conductingthe film squa once more over a drum k having a large diameter, so that astrong adhesive action is produced between the film and the supportingbase. The drum R: has a diameter of 1 meter and is equipped withpress-on bands m in the same manner as drum 6. After being released fromthis drum is the film is further conducted through the acid bath by thesmall rollers n, then through a water bath 0 and hereupon passed into aglycerine bath and then to a drying apparatus and a cutting device. Asthe appliances for this are well known to those skilled in the art amore detailed description is unnecessary.

By this means it is possible toproduce extremely thin cellulose hydratefilms as clear as glass with a weight of less than 15 grams per squaremeter. It is even possible with the greatest ease to make such films ofmerely l0, 8, 6 and even 5 grams in weight per square meter. Such thinstructures manufactured from coppercontaining cellulose solution andprecipitated in soda lye have quite a peculiar character. They areabsolutely transparent, and their presence in single film form isscarcely perceptible to the eye in certain positions. The structureshave lost the glass-like, brittle nature of known films. 'I'he foils areas extremely pliant as gold leaf; they are, therefore, especiallysuitable for covering foreign objects even with uneven surfaces. Withtheir unsurpassed fineness, pliability and great plasticity the foilsare capable of adapting themselves to and fitting all unevenness.

Their extremely low weight, their toughness and comparatively greatresistance make them ideally suited for covering and packing smallobjects with great surface, especially when a packing material isrequired that does not appreciably increase the weight of the package.

The foils can be crumpled by hand or by machine in operations and madecompletely smooth again. Whole foils or strips can be knotted likethreads, the knots undone and the foils or strips then smoothed again.

In speaking of a foil which is clear as glass, we mean a productconsisting of regenerated cellulose without bubbles, stripes and otherinternal structural irregularities. It is, however, possible, forexample by suitable additions, such as finely ground inorganic pigments,to deprive the foil of its character of being clear as glass, to make itnontransparent or opaque, or it may be dyed, either by subsequenttreatment or by adding corresponding substances directly to the spinningmaterial.

We claim:

1. Absolutely transparent cellulose hydrate foil substaTiiti'allyequallysmooth on both sides and manufactured from copper oxide ammoniumcellulose solution and having a weight per square meter of less than 5grams.

2. Extremely pliable cellulose hydrate foil substantially equally smoothon both sides and having a weight per square meter of less than 10grams.

3. Extremely pliable cellulose hydrate foil substantially equally smoothon both sides and having a weight per square meter of less than 5 gramsand capable of being crumpled and knotted and then smoothed out again tosubstantially its original condition.

4. A glass-clear film of regenerated cellulose which is uniformly smoothon both sides thereof and is produced from a copper oxide ammoniumcellulose solution, said film being of substantially; a uniform thinnessof less than 5 grams per me 'er.

5. A glass-clear film produced from a copper blow-holes, striations, orother internal structural oxide ammonium cellulose solution, said filmbeirregularities.

ing uniformly smooth on both sides thereof and 7. A transparent foil ofregenerated cellulose being of substantially a uniform thinness of lesswhich is substantially equally smooth on both than 15 grams per squaremeter. sides thereof and has a thickness no greater 5 6. A glass-clearfilm produced from a copper than corresponds to a weight of about 15grams oxide ammonium cellulose solution and being. of per square meter.

a substantially uniform thinness of less than 10 RUDOLF ETZKORN.

' grams per square meter, said film being free of EWALD KNEHE.

l P e 5 7 CERTIFICATE OF CORRECTION.

Patent No. 2 055,645. March 51, 1956.

RUDOLF ETZKORN, ET AL.

It is hereby certified that the name of the assignee in the abovenumbered patent was erroneously written and printed as "I P. BemberyAktiengesellsohaft" whereas said name should have been written andprinted as I P. Bemberg Aktiengesellsohaft, of Wuppertal-Oberbarmen,Germany, a corporation of Germany, as shown by the records ofassignments in this office; and that the said Letters Patent should beread with this Correction therein that the same may conform to therecord of the case in the Patent Office.

Signed and sealed this 12th day of May, A. D. 1936.

Leslie Frazer (Seal) Acting Commissioner of Patents.

